Organic or polymer light emitting device, O/PLED, may be used in building displays on flexible plastic film. The low work function metal cathode as well as the organic/polymer media used in these devices degrade extremely fast when exposed to O2 or H2O (oxygen or water). It becomes an especially severe problem when the device is built on a plastic substrate because of high permeability of O2/H2O through it. Therefore, to build a flexible display on plastic with a meaningful lifetime, a transparent hermetic barrier layer coating on the substrate becomes indispensable. A similar problem exists for RF (radio frequency) ID (identification) tags which use an antenna and an IC (integrated circuit), which may be a small block referred to as an NB disposed in a substrate which supports the antenna. In the case of an RF ID tag, it is desirable to attach an IC (which includes the RF receiving and transponding circuitry and the ID information, such as a serial number) and an antenna to a flexible (e.g. plastic) substrate which can then be attached to a product. Any seal or barrier layer should be RF transparent (otherwise the tag will not receive and transpond).
In addition to O/PLED display, many electronic devices, such as organic transistor or LCD displays, are or will be built on flexible plastic substrate in the future. These devices are also sensitive to H2O, O2, or other materials in the environment, and need a transparent barrier on plastic for protection.
Many transparent barrier materials suffer from the formation of pinholes during deposition. It is desirable to have a transparent barrier material that is resistant to the formation of pinholes through the entire barrier (particularly since the pinholes tend to propagate in the barrier material).
Many transparent barrier materials have a substantial content of organic materials, which can suffer from instability when exposed to ultraviolet or visible light, or oxidative materials such as ozone. It is advantageous to have a transparent barrier material with little or no content of organic materials, or to use organic materials that are insensitive to irradiation and oxidation.
Finally, in certain applications it is desirable that there is an easy means to pattern a transparent barrier layer. For example, if one wants to make an electrical connection or via through a barrier layer there must be some way to etch the barrier selectively. To date, many of the transparent barrier layer materials are not easily etchable with conventional wet and dry etch chemistry. An example in the art of a transparent barrier layer used for O/PLED devices is represented by so a called “Vitex” film, which is typically a multi-stack of plastic/Al2O3 layers. Several problems are associated with this type of barrier film. First, it is difficult to either wet or dry etch through the film, making it difficult to form electrical contacts through it. For a display backplane which contains many ICs, where many vias have to be made through the barrier layer for contacts between the ICs and electrodes, or, for a top O/PLED barrier layer, where electric contacts have to be made between electrodes and power supplier after barrier deposition, dry etching through Vitex is challenging. It would require either expensive high-energy plasma equipment or corrosive Chlorine containing gases. Second, it tends to form bubbles when the film is extensively exposed to UV/Ozone or O2 plasma due to decomposition of the plastic layer in the stack. Since UV/Ozone or O2 plasma exposure are the most effective means to clean ITO anode before the spinning of a hole transport layer, achieving a properly cleaned ITO surface without compromising the integrity of the underlying Vitex layer becomes very difficult.